also known as drive-in; concentration of diffusant (dopant) on the surface decreases during the diffusion process, i.e. while some dopant atoms diffuse into the substrate no new dopant atoms are supplied to the surface of the wafer.

drive in

high temperature (>800 oC) operation performed on semiconductor wafer in an inert ambient; causes motion of dopant atoms in semiconductor in the direction of concentration gradient (diffusion); used to drive dopant atoms deeper into semiconductor.